In-situ preparation of macroporous network of silicalite-1 nanocrystallites

Abstract

Large macroporous networks of silicalite-1 nanocrystallites have been produced from the in-situ hydrolysis of tetraethoxysilane (TEOS) in the presence of concentrated solutions of both molecular (tetrapropylammonium) and polymeric (monodispersed polystyrene beads, ∼400 nm) templating agents followed by hydrothermal and calcination treatments. The morphology of these solids has been characterized using SEM, HREM, XRD, ²⁹Si MAS-NMR, nitrogen adsorption–desorption and mercury intrusion techniques. It consists in a somewhat regular array of nanocrystals (∼100 nm) of silicalite-1 (pore size is ca. 6 nm) organized around interconnected macropores of narrow size distribution (330 ± 30 nm). As silicalite-1 crystals are grown into macropores’ walls, a secondary network of mesoscopic voids is formed between the crystallites (25 ± 15 nm). Two out of these three levels of porosity are narrow distributed.